Television system



Oct. 9,I 1951 o. H. SCHADE 2,570,723

TELEVISION SYSTEM Filed Nov. 21, 1946 2 Sheets- Hee?. l

ATTORNEY Oct. 9, 1951 o, H, SCHADE 2,570,723

TELEVISION SYSTEM Filed Nov. 2l, 1946 2 Sheets-Sheet 2 mieu l l lili BLUE lNvEN'ToR OTTO H. SCHADE ATTORNEY Patented Oct. 9, IQSI a Y TELEVISION SYSTEM Otto H. Schade, West Caldwell, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application November l21, 1946, Serial No. 711,235

1 The present invention relates to television, and, more particularly, to the method of and means for operating a television transmitter so that color television signals may be so generated and transmitted that, when received, there will result the production of color television images of high fidelity and of a high order of color purity.

In color television transmitting systems of theA sequential type, television signals representative of the various color components of the subject' matter are sequentially transmitted. When these signals are received at the television receiver and images are reproduced on the receiver image tube, colored images will be observed when the produced images at the receiver tube are viewed through an appropriate light filter arrangement. It is common practice, at 'present,.in color tele-v vision, to employ tricolor sequential operation Where the three primary colors or components are chosen as red, blue `and green. Television signals representative of these individual color components are sequentially transmitted and theY switching rate between the three colors is gen-- erally chosen at a frequency such that a 'minimum, or substantially negligible amount of iiicker will be produced at the receiver. In color television systems, it is generally customary to scan each successive eld in a diierent color so that the color switching rate corresponds to the field frequency and it is also common practice to utilize the black and white technique of double vresponsive electrode of the television pick-up tube causes corresponding charge images to be built up within the tube and when these charge images are scanned by the cathode ray beam generated Within the tube,'television signals corresponding to the intensity of the charge image are produced. In order that the .charge image may develop or accumulate to a maximum extent pursuant tothe intensity of the light available orprovided, it has generally been the practice to permit light to be projected upon each particular portion of the light responsive elec- 15 claims.'Y (ci. 17a-5.2)

trode for a maximum length of time between successive scanning operations and to then scanA the resulting charge image` by the cathode ray beam developed in the television pick-up tube .thereby to produce video signals corresponding to the intensity of light of the particular color.-

In order that the television pick-up tube will have a maximum length of time Within which to develop a charge image, the scanning operation of the cathode ray beam has heretofore been so controlled with respect to the color lter assembly that the position of the scanning cathode ray beam coincides with the line of demarcation between successive lter elements of the color lter assembly used at the transmitter. Furthermore, this particular phase relationship between the scanning cathode ray beam and colory lter assemblyynamely, maintaining the beam spot position coincident with the line of demarcation between filters or in the region between successive filter `segments of the lcolor lterassembly at the pick-up tube, has been proposed by the prior art in order that the light responsive electrode of the television pick-up tube will be exposed to light of only one color for the field cycle immediately preceding each scanning operation. New charge images Will then be produced, between each successive scanning operation, that represent the light intensity of one color component only.

Generally, the lter assembly (which may, for

example, be made in the form of a disc, a drumv or a truncated cone) is provided with a plurality of filter elements (normally red, blue and green) and between these lter elements is generallyV provided a spoke or light opaque member serving the purposes of supporting the individual filter elements and of producing an optical shadow of a 'predetermined vertical width extending hori-` xzontally across the light responsive electrode of the pick-up tube.A As explained above, it has been customary,l especially with pick-up tubes exhibiting full storage characteristics, to so phase the rotation of the color filter assembly with respect to the vertical deflection of the scanning cathode ray beam that the progression of the shadows of the spokes across the light responsive electrode corresponds in position and occurs .simultaneous with the progression of the scanning cathode ray-beam across the target electrode so that scanning operation takes place at all times in the shadow of the spoke or opaque memberbetween adjacent filter elements. With thisphase relationship thelight responsive elec-` trodes will have been exposed to only one color component prior to each scanning operation with When the color lter assembly isphasd 'tith` respect to the scanning cathode ray beam as indicated above, such that the scanning operation takes place in the shadow of the spoker` a minimum amount of color carry-over or color contamination Will result from thesrtanrdpoint `of color of light to which the transmitting tubfe'is subjected between successive scanning operations however, it has been found thata certain amount of color contamination 'or lack'of *color fidelity still remains by reason of thev storage characteristics of the television pick-up or camera tube.-v Color contaminationor lack of color fidelityhmay, therefore, Aresult fiionrr'nrie r"anoth`er o ftwo general effects, namely; (l) by reasonof improper phase relationship Yof the color `filter assembly with respect to the scanning operation, and (r2) wby reason of the storage characteristics ofvthe storage type television pick-up tube.

A.To illustrate the first type of color carry-over or. l a ck of color fidelity, if, in "a pick-up tube operatingatrlOO per cent storage, the phase relationship of the 'lter assembly andthe scanning cathode ray beamshould be /such that the scanning operation occurs slightly'in advance Vof the spole orjpointof junction of two adjacent filters then color purity cannot'beinaintai'ned. For example,let it be assumedthat the colorsequence is red, b lueandgreen and that the scanning operation takes place `near the trailing edge of the red filter but ahead of or preceding the spoke orwjunctionrof the red and the'ne'i'it succeeding blue lter. Signalswill beprdied which correspondto the red color coinpfonnt'but after the scanning operation vsorne light"vvill still be permittedfto reachthe light responsive electrode through the 'remaining or trailing'portion of `the red filter. This red light Will vproduce a corresponding charge onthe target lectrode of the television pick-up tube. v'As the'filter assembly is -furtherrotated light will then beftransmitted to the light responsive Velectrode, vthrough the blue element vof the filter Iassembly toproduce further charges. During the scanning operation ofthe next succeeding field, which is presumably the bluejfV field and which occurs n'e'ar the trailing edge of the blue lter but ahead of or preceding the spoke or junction of the blue and the next succeeding greenl lte'n'video Ysignals will be generated. vWhen these signals 'are transmitted to the receiver and,there'sulting imageis viewed4 through a blue lilte'r element, the low intensity signals from the redV portions of the image will cause these red portions or objects tocv have a bluish tinge as 'a result'of their being made visible through vthe blue'lter at the "receiver due to thatrpo'rtion of the red lter'at the transmitter that trailed 'r'follosfed the scanning beam.V By phasing the colofr'nlter assembly such that the light responsive electrode is e'xposed to light of one color only betweena'succe'ssive light scanning operations, this type of color carry-over or lack of color fidelity may beeliminated. I Y A In the other type of color'carry-over, namely that produced as a result of the storagecharacteristics of the television pick-up tube, a diierent effect takes place. -Instorage pick-up tubes 4 and especially in systems Where interlaced scanYJ ning is employed, the entire electrostatic charge produced on the target electrode is not removed by a single field scanning operation. After each scanning operation, there is a certain percentage or residue of charge on the target electrode, the extent of the residue depending upon the characteristics of thetube, the capacity of the target electrode, "secondary electron redistribution (in the iconoscope and image orthicon), beam spot diameter, and various other factors. This resildiie of charge, unless cancelled by special means Lor by se'condaryrelectron redistribution, when removed by theneXt eld scanning operation, re-

rsiil'tsintl'ie production of signals at least partially representative ofthe preceding color component and when such signals produce a television image at'the 'receiver and the image is viewed through amcolor lter of a different color, contamination or lack of color fidelity results. There have been proposals or special means to eliminate color daifryover or lack of color jfldelity by reason lof stage characteristics of thetelevisio'n pick-up tube 'such 'as 'fare shown anddescrbed, for eX- arnpl'e, inmy Patent No. 2,458,649, supra, Wherein it is proposed Athat the scanning cathode ray beam, bri'itsretu'rnfdeection stroke, be utilized forcompletingthe discharge of the target elec'- trode..

lack of'cdlor fidelity by reasonY of colorcarryover dueto the storage characteristics of -tele'- visioh pick-'up tube's'causes red images to have afbl'uish'tinge, blue imagestohave a green tingeV particular 'contamination exists `when the colorv sequence is red,blue, green. If'the sequenceis changed tored, green, blue,y for instance, then the contamination still `exists but in different colors. yRegardless of the sequence, a lack of true 4color fidelity exists by reason of the storage characteristics of the pick-up or Vcamera tube andthe fact that the charge image is not complfetelyk removed by a single eld scanning operati'n. vThis typeofcolor contamination remains even though color contaminatiomso far as phase relationship of the flterassembly is concerned, reduced to a minimum byahaving the scanning opfifatn take place in Ithe shadow of the spoke inthe case 'of fullvstorage pick-up tubes. In some present day television pick-up tubes. the amount "of the residual signal or residue can be reduced by proper design and use and is not large but may amount to some 5 to 15% depending upon the amount of charge remaining within the Vtube after each field scanning cycle. Y

In describing the present invention, it will be assumed 'thata sequence of red, blue, green is employed. `With this sequence the above refferred to type of color contamination or lackof' for garnple, to appear bluish. Under such con-V ditions, if a srnall amount of green could b'e added, the small percentage of green and the undesired blue, when combined with the principal fred color, would Aresultin a small percentageof White light with the remainder `a pure unadulterated red color. This blending would result ina small'percentage of -White light which actually would correct the chroma of the produced color images by reducing their often too vivid intensity inasmuch as the White signals of akinescope or television receiver image tube are somewhatexpanded'by reason of the electron gun characteristics of the K inescope. This addition off-a small White component Will therefore,

in eiect, tend to improve the gamma and will Y* result in an improvement in the chroma in the reproduced image especially in flesh tone values. Accordingly, if a small amount of green could be combined with the undesired small amount of blue present when red objects are observed, and similarly a small amount of red and blue combined with the undesired small amount of green and red present when blue and green objects, respectively, are observed, then the lack of color delity could be completely overcome with the result that color television images of a high degree of color fidelity could be produced at a receiver.

In accordance with the present invention, this result is accomplished and small percentages of dilferent colors are combined such that the undesired color tones that are present due to charge carry-over are completely neutralized. For eX- ample, when red images appear slightly bluish due to the characteristics of a storage operated television pick-up tube, a small compensating amount of green is deliberately added so that the added greenish component will react to overcome the undesired yet present bluish component. The same is true with respect to blue objects which are inherently caused to appear greenish by reason of the storage characteristics of the television pick-up tube and a small amount of red is deliberately added to compensate for the undesired greenish tinge. Similarly, green objects inherently appear slightly reddish but when a small component of blue is deliberately added,

`a slightly lighter pure green color results and substantially complete color fidelity is restored.

In accordance with the present invention, the deliberate addition of the appropriate colors to compensate for the lack of color fidelity due to the charge storage characteristic of television pick-up tubes exhibiting full storage characteristics is accomplished by proper phasing of the color filter assembly at the transmitter with respect to the scanning cathode ray beam such that the scanning operation no longer occurs within the shadow of the spoke or exactly in coincidence with the line of demarcation between lter elements as was the case with systems heretofore used, but, instead, occurs slightly subsequent or following the spoke or 'line of demarcation. The extent to which the beam follows the spoke or line of separation between lter elements depends upon the degree of color mixing required in order to compensate for color carry-over due to storage. Accordingly, the light responsive electrode of the television pick-up tube is permitted to have 'projected thereon a small amount of light through a lter segment having a color different from the color through which the light responsive electrode receives its principal exposure.

It is, therefore, one purpose of the present invention to provide, in a color television trans-V mitter in which television pick-up tubes of thefull storage type are employed and in which a lack of color fidelity is present due to the storage so that the resultant image scanned.

A still further purpose of the present invention resides in the provision of means whereby the -fphase relationship of the color filter assembly at the transmitter as compared with the vertical deflection of the cathode ray beam in its scanning A operation, are such that the scanning cathode ray p beam follows, by a predetermined small amount,

the line of demarcation cr spoke separating adjacent lter segments.

A still further purpose of the present invention resides in the operation of a color television transmitter in such a manner that a high degree of l color fidelity results and furthermore the operation of the transmitter in such a manner that the chroma of the reproduced image is materially improved.v

and of adjustable magnitude, are produced during the field cycle immediately preceding the 'field in which the principal video signals for that e particular color component are produced.

Various other purposes and advantages of the present invention will become more apparent to those skilled in the art fqrom the following detailed description,- particularly when considered in conjunction with the drawings where like reference numbers represent like parts and wherein: 1

Figure 1 represents a development of a color filter assembly used in explaining the theory of operation of the present invention;

Figure 2 represents a colored object area to be scanned;

Figure 3 represents schematically the video signals produced when the object area of Figure 2 is scanned with the scanning cathode ray beam maintained at the line of separation between adjacent filter segments of color filter assembly; s

Figure 4 represents schematically the colored image reproduced at a television receiver from the video signals of Figure 3;

Figure 5 represents schematically the videol signals produced as a result of scanning the ob-` ject area of Figure 2 in accordance with the pres-V ent invention with the scanning operation occurring slightly behind or following the line of separation or demarcation between color lter segments of the color lter assembly;

Figure 6 represents schematically the colored image reproduced at a television receiver as a result of video signals shown in Figure 5;

Figure 'Tshows schematically the color television transmitter and receiver; and,

Figures 8 through 12 show developments of various forms of color filter assemblies that may be used in-conjunction with the present invention.

Referring now to the drawings and more particularly to Figure 1 thereof, there is shown a development of a color filter assembly which for; the purpose of this explanation may be considered as a disc, a drum, a truncated cone or similar unit which may be used at a television transisa more accurate f. representation in color of the subject matter mitter' for the transmission of color television images-'in a sequential system. lThe -llter =as sembly 4represented in Figure 1 shows the use of three diierent component-color lters, namely, red, "blue and green,V and for the purpose of this description, it Will'be assumed vthat these three colorv components are used "although Within the broad' teachings of this invention other combinationsof colors and a diierent number of color components may be employed Where expedient. In Figure 1 the red, blue and green filters are represented at 3, 6 and 8, respectively, With red and `blue -repeated at I'S and I2. Actually the iilter assembly `may include only one set of lters'or-a pluralityoi sets may be included therein, depending upon 'the size of the assembly. The'directicn of movement of the lter is represented bythe arrow 15 and with this direction of movement, the sequence or order of the colors is red; blue, green.

Itis to be understood by those yskilled `in the art that the color lter assembly is positioned theoptical light path oi the television pick-up tubeor camera and in accordance with present practice, the rotational vspeed of the assembly is such fthat a diierent color filter is interposed in the-'optical axis for each successive and diierent television color iield. Accordingly, 120 'elds per second is the vvertical deflection rate of scanning in the television pick-up tube, then an appropriate color iilter assembly having, for example, six iilter segments (such as the illustratively suggested disc shown at Il in Figure I'1) would rotate at 1200 R.P. lVI. (20 revolutions per second). `In Figure 7 a motor I8 is provided for rotating the disc (or drum) at the desired rate andthe disc Il is positioned in the optical light path --of the lens I9 of the television camera. If a'disc fis employed, then it is possible that the spokes or lines of separation between lter elements may be curved as shown in Somers Patent 2,429,849, issued October 28, 1947, for example. The degree of curvature and particular shape depends upon the size of the disc and the location of the center of the disc relative to the scanned area.

In Figure '7 the television camera and all "ancillary equipment, including the transmitter, are represented generally at 2i! from which a modulated carieris conveyed to any desired communication `channel and may be transmitted from the antenna 2l or fed out through a coaxial line or cable, Where desired. A phase control device 2`2 'is also used at the transmitter for aording a meansfor shifting the phase relationship of the disc Il (or filter assembly) With respect .to the vertical deection of the cathode ray beam. Although rthe phase control is shown as operatingon the drive motor i8 of the disc I1, it is also entirely vpossibieto charge the phase relationship by shifting the phase of the timingpulse for the vertical deflection of the cathode ray beam to cause itlto vbeadvanced. or delayed by a predetermined amount -With respect to Ithe lter disc, the rotation of which could be held constant. Alternatively, the drive motorstator may be so supported vas to permit itto be rotated manually toeiectvthe desired phase relationship. As the disc Ifl is rotated in front of the television pickup r-camera, television signals .are generatedfor each eld representing, in succession, the light valuesof the'red, blue and green color components ofthe object area;

.The Vtransmitting signals are received bya receiving .antenna 24 .or other receivngmedium and are supplied to a television receiver repr sented generally at These signals when' properly amplified and demodulated produce a black and White image on the endof the cathode ray tube or kinescope 26. Positioned in front of the receiving tube 26 is a rotatable color filter disc 27 which included appropriate filter segments-and which is rotated at a speed such that a different filter segment is interposed in iront of the receiving tube for each television eld.

AThe observer or viewer then views the produced succession of black and White images through the filter segments of the disc or lter element V21 in sequence, thereby imparting to the image Lby Well known multi-color additive processes Aand principles the visual impression of full color. The disc at the receiver is driven by a motor 2'8 at an appropriate rate of speed and both the speed and the phase may be controlled byequipment located within the television receiver V25.

Thefcontrolling factor is that the optical image or the receiver may be replaced by appropriate drums, truncated cones er any other type of colorV filter assembly. Regardless of the particular type 0f color lilter assembly employed it is desirable that the line of separation or junction of the elements be maintained substantially parallel to the line or horizontal dei'iection oi the cathode ray beam. This is particularly true at the transmitter in exercising the present inventicn as will be appreciated later. Furthermore, although a'radio transmission is described above, actually the transmitter and receiver may be connected by coaxial cables or other appropriate connections.

In Figure 2 of the drawings is shown an object area 30, which, for the purpose of the description of this invention Will be assumed to be the colored subject matter transmitted. Through the choice of such an object the purposes and advantages of the present invention may be more readily described and understood, although naturally a television system including the present invention is adapted for the transmission of any colored object either by direct pick-up (as in a studio) or through the use of colored slides or ilm. The arrow 3| represents the direction in which the cathode ray beam electivelylscans the object area and for the purpose of this description the directionof beam deflection in the line or horizontal direction is immaterial.

As explained above, it has heretofore been the practice, in sequential color transmissions, to so phase the color iilter assembly with respect to the vertical scanning operation that the cathode .ray beam scans the target area in the region of the shadow cast by the spoke between successive iil- The color lter assembly of Figure 1 includes not atpica o nlyvthev filter elements per se but, to assist in the explanation of the present invention, spokes or opaque portions are included between adjacent' filter elements. These spokes or opaque areas are schematically represented at 5, 1, 9,

vopaquerportion between adjacent iilter elements (as has been the usual practice) in order that there will be no lack of color fidelity or color carryover due to the lightresponsive electrode of `A takes place in the shadow cast by the spoke or the pick-up tube being exposed to light of more than one `color between successive eld scanning operations. Furthermore, the object to be scanned will be that represented at Figure 2. Figure 3 shows schematically the video signals thatwill begenerated and transmitted under these ,con-

ditions. The amplitudes of the Video signals represented in Figure 3 are arbitrary and are chosen primarily to assist in an explanation of the invention. When` an object area such as that represented in Figure 2 is placed in front of a color television pick-up camera with which is associated a color lter assembly such as represent- Aed in the developed'orm of Figure 1, video signals such as represented in Figure 3 will be developed -if the scanning operation takes place in the shadow of the spoke, i. e., under the shadow cast by the opaque portions betweensuccessive filter elements of the colorA filter assembly. vFor example, under this condition of phasing, the dot 34 represents the vertical position ofthe scanning cathode ray beam relative to the color filter assembly, and when the beam is deflected horizontally it remains under the shadow cast by the opaque portions 5 of the color filter assembly. The vertical deflection rate of the cathode ray beam across the target electrode and the rate of progressionr of the shadow of the spoke '5 across the light responsive electrode of the pick-up tube are substantially identical so that during one complete Vertical deflection on one television eld, the entire scanning operation for that field takes place in the shadow of the opaque portion 5. Elements of the target electrode will, prior to scanning,v have developed an electrostatic charge corresponding in intensity to the intensity of the red component of the object area since the preceding iilter of the filter assembly is red. During the scanning of the object area 30, the red filter element 4 will permit light from the top white portion to be projected onto a corresponding portion of the light responsive electrode,

--of the television pick-up tube through the red filter and as a result, the corresponding portion ofthe target electrode of the pick-up tube will contain no charge representation, for all 10 practical purposes, so that no Video signals corresponding to blue will be generated during this eld as indicated at 53 in Figure 3. The green portion of the object area 30 has not supplied any light to the light responsive electrode of the pickup tube through the red filter 4 but signals of low intensity as represented at 54 in Figure 3 will in fact be generated for a reason which was referred to above and which will be explained more fully later. Lastly the lower light portion of the object area 30 will produce video -signals as represented at 55 in Figure 3.

This completes the scanning of one iield, whereupon the cathode ray beam is returned rapidly in a vertical direction to begin the scanning operation of the next succeeding field. The cathode ray beam is blanked out or otherwise prevented from removing charges that are present on the target electrode during this return vertical deiiection. During the next succeeding eld cyclev the vertical position of the scanning spot or beam with respect to the iilter assembly is represented at 36 in Figure 1 and during the entire scanning operation for this neld the beam, in both its horizontal and vertical deflections, remains in the shadow of the opaque portion 'l of the color lter assembly shown in Figure 1. During the scanning of the tcp white portion of the target area 30 color signals will be generated which are represented at 5S. The next portion .of the object area is red and light from this portion will not have been transmitted throughthe immediately preceding blue lter t with the result that the light responsive electrode, for all practical purposes, has not been exposed to any light over that portion corresponding to the red part of the object area. Ideally,V therefore, no television signals should be generated yet actually low intensity signals are in fact generated as represented at 51 in Figure 3 during the scanning of the portion of the target electrode corresponding to the red part of the object area. The reason for the generation of these signals is based on the characteristics of storage type pick-.up tubes which may have a or complete storage characteristics, or the storage may be considerably less than 100% depending upon the particular .design and construction of the tube.v In either ,caseJ the entire charge on the target electrode caused by exposure of the red portion of the object, area through the red filter 4 in the preceding `iield has not been removed Yby the single preceding field scanning operation which produced the signa'ls represented at 52 in Figure 3. This is due lto several factors, one of which may be attributed to the interlaced scanning normally employed, and the fact that inter-line charges are not so completely removed as are the line charges by the scanning operation; the size or diameter of the scanning spot, ras'well as other factors. Even if interlaced scanning is not employed, some residual charge will still remain in high resolution pick-up tubes because of incomplete discharge of small charges by low velocity electrons either Ain the discharge (or scanning) beam or by redistribution of secondary electrons. It is this -residue of charge, after one field scanning cycle, that permits the production of the low intensity lsignals 51 on that portion of the target electrode lcorresponding to the red part of the target area where, in fact, no television signals should be generated if complete delity of color isv to be obtained. Following this, the blue portion of the object area will cause video signals, repre? different colors are producedv at sented at 58l in Figiil'e to be produced since lfl'ghfrom hebll'lefpoton of thev (Jhl'eol'ftlv will have been freely'trarls'lrnittedV through the Ibliie iilter G to permitY theproductionfof a charge on the target electrode. 'Zi'nfev scanning of the portioncorrespondingfto tl'ie greeipartbf the ob'- jectfS Will result in the'production of substantially no video signals 'as representedat- 5,9 in Figure 3 sincevtheN light from`tlie green"portion 'ofthe object area was blocked lby lootntlaeV` preceding red 'andbluefllters 4 and 6. The bottom .white portion willnaturally result in the production of video"signals asrepresented atv SQ, During Vthe'scanr'iing' of the next television field, the` vertical position of the cathode ray beam is represented Val'fv'f and the be'am'in'both its'hoizontal "and` vertical deflections remains in' the shadow cast'by the opaque portion; 3z following theY green lter 8. andJ precedingthe red lter IB. During thescanningwof thism'fieli'television signals will be"generated,corresponding to the top white portion, theg ,enpr'irtioifiI and the bottom white portion of 'the' object area agropr'esented at l, e4 and, 'respectively'in Figure 3, While low intensity signals, 53Y inY Figure, will be generatedfo'r therme' portion of the object area 3l! due to'inoornplete cancellation of the charges producedn'the target electrodeY during the immediately prec'edingeld cycle. Substantially no Video signals" will begenerated during the scanning' of the red portion of the object area as'i'ndicatedatv 62 in Figure 3. y

During the next suecfclingl television field, the cathode ray/'beam' or -scanning sport wili be located,I in phase relationship, "as indicated at QQ in Figure 1 and during' lthisffield, signals vwill be generated as represented'aj; through lit of Figure'. This is, for allpractical. purposes, the red field. but, in addition, llow`'iriterislity signals corresponding to thegreelnportion ofthe object area will also be genegatedfas indicated at iis, since the immediately preceding lield scanned was green. It willlalsb Iloe"observedthat the Sign nals generated duringA thislfieldlale identical to those generatedduring the scanning ofthe first described eldwith tliescanningvspolt locatedas represented at .34, and with videe signals 5l thfTOugh 55 beingfgenrated.

In television receivers, it is, Vat present, theY usual practice to provide` a `rotating or moving color filter-assembly and toreproduce the image preferably in black andzwhiteonnthe,viewing end of a kinescope or receiving tube, The lters are sequentially interposedv between the observer and the produced blackA and white image in order to irrpart color to the irnagesin Sequence.' For the purpose of the present invention, itwilljbe assumed that such a construction Ais `usedland that the phasing of the discwas suchv that a filterv segment of appropriate color will be positioned over the area rendered luminous or iiuorescent by the action of thecatllode ray beam. The'color of the lter segmentthat is in position in front of. the activated portion ofthe receiver tube` screen should, of course, correspondfin V'color to the filter segment which was used in exposing the photo-cathode of `thepick-up tubeiustprior to the particular field scanning cycle;L The present invention, however, is lactually applicable to receivers wherein no disc on moving, filterassembly is provided but instead wherein superimposed screensof .diliferent phosphors are used or the type receiver WhrePafe maQf different .arcas In Figure 3 is represented kinescope viewing filters 14, '16,78 and' 'offcdlors'red, bllie, gr,

red, respectively, 'andV these filters, as will be obiserved, are associated individuallyv with parti'cilar field vintervals ofy the'vid'eo signalsshownl in Figure 3. The red kinescope viewing filtei` "I4 is, for example, associated, with.v videoV signals 5J through 55 whichare generated by scanningfin theshadow of the opaqueV portion?,` immediately following the red lt'er 4f' Sirriilarly, re'ceivcger image'vi'ewing filters 16, 1.8, of-Fig'ure'B corfresponds to Similar color' filters'V B, `8 .and ll 0 of the transmitter filter assembly. The video represented in Figure 3, whena'pplied to a tele,- vision receiving tube,v pro'duce'black'fand white images to which are imparted 'color'sfby the l'ters 14 through 80A through whichthese nirrlages are observed in sequence, Therelationshipfof time to the video signals and the order of the lters yis represented by the arrow inFigure 3A. Since the .top andbottorn portions` of the object cause illumination on thegcorresponding portions ofthe receiving tube in each eld, and are, visible through each of the red, bluerand green. ltel's iny succession, the optical eiTect is thatof a reproduction of white'light, since thesethree colors are additive and the useof proper filter numbers are chosen in'acccrda'nce with the phosphors or luminescent material of the receiving tube so that substantially white light can be produced. The reproduced image, asY it( appears at the rreceiver, is shown inFigurel fiand in this iigure, the composite colors are represented in a horizontal direction, all of which are uniformlyapplicable to the samehorizontal-portion ofv the object, as, for example, the red, blue and green portions, which additively'cause the top portion ofthe viewed iroage to appearwhite, are represented at 8l, 82 andBB. A-similar situation exists withv'respect to the bottom white portion of the object.

The red portion ofthe object area 3!) was effective to produce normal intensity video signals,; 5,2 for the field during which the scanning operation took place in the shadowrof the spoke 5. This caused the corresponding portion of the screen of .the receiving tube to emit'white light, which, when observed through the redfilter 14, caused that Vportionof the screen to appear red. This coloration is represented at` 84 in Figure 4. It will beobserved, however,l that some signals were developed during the scanning of the portion of the target electrode corresponding to therred part of the object area during thelnext succeeding field (blue) eveny though no light hadbeen projected onthe corresponding vportion of the pickup tube during the immediately preceding iield cycle just prior to thescanning operation in the shadow of the opaque portion 1. These, signals as explained above, are represented at 51 in Figures. These low intensity signals cause a small amount of white light to be emitted from Vthat portion of the receiving tubeY correspond'- ingtothe red part of the object butV during-this eld cycle interval, theobjectis seen through the blue filter 16,in order thatrtheblue portion of the object will be seen as .blue as represented at 85 in Figure 4. Theobservation of the small amount of light from thatportiony of the receiving` tubecorresponding tothe red portionrof the object through the blue filter results ein the red portion assuming. in addition, a bluish tinge arid thstluish'tinge is(.yrepresenteciiatW s6 Figure@ Theirnageproduced vand seen bythe bsfver at'A theveverj "therefore, 'rather than I3 appearing a pure red, as in the object, is, in fact, '-'red plus a small percentage of blue due to the residual signal 51 producing light which is visible fthrough the blue lter. 1 A similar effect takes place insofar as the blue portion of the object is concerned. Its principal yfcoloration is due to the signals 58 and their eiect vbeing observed through the blue lter '16.r The `'low intensity signals 63 generated in the next --ield cycle cause low intensity light to be emitted over that portion of the receiving tube corre-f'- spending to blue, but at that time, a green lter in front of the .receiving tube with the result that a small or low intensity green coloration 81, in Figure 4, is added to that portion of the receiving tube corresponding to blue in the'object *areapwith the result that blue objects are given -a greenish tinge. By similar action, green objects, when viewed at the receiver, appear principally green as indicated at 88 in Figure 4, with .asmall component of red as represented at 89."

`scanning cycles, and even though the light re- "'sponsive electrode of the television full storage 'pick-up tube is subjected to light of one color only between successive eld scanning cycles, 'complete color delity reproductionA is impossible by reason of the retention of the chargei in the Vtelevision pick-up tube from one eldl F into the next succeedingl field.` If the color "sequence is red, blue, green, as is assumed in the above description, then red objects have a slightly bluish tinge, blue objects a slight greenish tinge and green objects a slight reddish tinge. 1A reversal of the color sequence to red, green, blue naturally does not eliminate the eiectvbut "merely alters the type of color indelity by vmalcing red objects appear greenish, `green objects lappear bluish and blue objects appear reddish.

Accordingly, in the present invention, this 4Vcolor contamination or lack of color delity is, 'in effect, eliminated by compensating color blending through the deliberate introduction of still;

'a third color with the result that complete color Vdelity is restored and a desirable small white Vcomponent is added. For example, as explained above, red objects appear with a slight bluish Ytinge which is particularly objectionable in therfl `reproduction of ilesh or facial tones, but if-a small and proper percentage of green can be added to the bluish red, the result is red with a small component of white. It may appear that 'Hand a dilution of tones, but, in practice, it has been found that such is not the case, but instead, the chroma is, in fact, improved and the `hue made more natural. One objection to color y i4 during these four cycles. The object area scanned is the same' object'as described above in connection with Figure 3 and as shown in Figure 2. The fields scanned will likewise be the same. v

In accordance with the present invention, it will be assumed that the position of the cathode ray beam is as indicated at 44 which is slightly delayed in position with respect to the opaque portionA 5, or line of separation, between the red and blue filters 4 and 6 respectively. Naturally the cathode ray beam is deflected in a horizontal or line direction during the scanning operation but the relative position of the beam and the opaque portion is maintained throughf out the scanning cycle. The scanning spot remains at substantially this predetermined distance trailing or following the opaque portiony 5 throughout the complete field scanning cycle as the scanning cathode ray beam is deflected horizontally` and vertically. If the scanning operation is performed with this phase relationship between the color filter assembly and the scanning cathode ray beam, then video signals corresponding to 9| through 95 in Figure 5 will be generated. Signals Sl and 95 will naturally be generated corresponding to the top and bottom white portions of the object area- 38 since white`- light from both these areas permits the transmission of light components through any lter element of the lter assembly. Video signals represented at 92 will be` generated corresponding to the red portion of the object area since light from this red portion will have been transmitted through the lter element 4 to produce an electrostatic charge image on the corresponding portion of the target electrode. During the scanning of that part of the target portion 5, and since this trailingoccurs within 'this would result in a washing ou of all colors 52;.-

. television has been that the colors are unnatural-.3,

"cycles and the television video signals generated the blue lter element 6, a small charge will be produced on that portion of the target electrode corresponding to the blue part of the object area, resulting in the video signals 93. Duringl the scanning of that portion of the target electrode corresponding tothe green part of the object area, low intensity'signals 94 will be generated due to the characteristics of the televisionpickup tube and incomplete discharge by one field scanning cycle, as explained above. After vthe field cycle has beencompleted, the cathode yray beamis then returned in a vertical direction Itf'o begin a subsequent field cycle, during which scanning -operation or cycle rthe cathode ray 'spoke 'l as` indicated at 46 in Figure l.

beam will VVoccupy a position relative to` .the During this field cycle, video signals will be generated corresponding to the top whitepart ofthe object area. `During the scanning of vthat portion 4of *the target electrode corresponding` to thefrejd part of the object area low intensity signals will be generated since the previously produced electrostatic charge image will'not have been completely removed by the action of the scanning beam or by secondary Aelectron redistribution ,in the immediately'.- preceding Iield cycle. These low intensity video `Signalsare representedv at 9].

f5 yWhen that portion of the target electrode corresponding to the blue part of the object.- area is scanned, video signals` 98 Will be generated since light Will have been freely transmitted from that part of the object through'therblue ilter 8 to produce corresponding electrostatic charges. During the scanning of.V the portion of the target electrode corresponding to the green part of the target electrode low intensity video signals as represented at 99 Will be generated by reason ofthe short exposure of thelight responsive electrode to light from the green part ofthe object area through the small portion of the green filter 8 which precedes, in point of time, the relative vertical position of the scanning cathode ray beam as indicated atV 46'. Finally, in this particular eld, video signals Hmwill be generated during the scanning of that portion of the target' electrode that corresponds to the bottom YWhite portion of the object area 30.

During the next field cycle, the relative vertical position of the scanning cathode ray beam throughout each line Will be that indicated at 48 in Figure 1, Which position is located slightly following the opaque portion 9 separating the green filter 8 Vand the red lter IIJ. Duringthis eld cycle video signals through |05 Will be generated corresponding to the various parts of the object area 30. With the scanning beam at the vertical position indicated at 48, and with this phase relationship, videoV signals represented at |0|, |04, and IOS-Will be generated corresponding respectively to the top White, the green and the bottom White portionsy of the object area. The low intensity video signals |93, corresponding to the blue portion of the object area-Will be generated due to charge carryover in thepick-up tube (similar to signals [i3v ine-Figure 3). The low intensity signals |02, corresponding to the red. portion of the object area will be generated Yby reason of the4 phase relationship of the lter assembly with respect to the scanning beam and the fact that a small part of` the red lter Il] precedes the beam when the latter is in posias indicated at 59 in Figure l, video signals: corresponding, for example, to HIE through H0 of Figure 5 Will be generated. These are a repetition of video signals 9| through 95 since in each eld the scanning operation trails the line of demarcation between` a red and a blue lter` element.

Associatedwith the video. signals shown in Figure 5 are kinescope viewing filters H4, H6, |'|8 and |20 which are the red, blue, green and red filter elements of the receiver color filter assembly 21. green. and red lter elements 4, 6, 8 and. i9 of the transmitter filter assembly of Figure 1 (or as shown at |1 in Figure 7); When the videosignals 9| through 95 produce a black and White image on the television receiving tube, and when this image is viewed through the red lter segment I4, lighted portion of the receiver tube dish tone due to the low intensity video signals These correspond to the red,v blue,

Y ingseld scanning cycle.

,93 produced asa result of the trailingl of the cathode ray beam: behind the line of separation between the red and blue'lters 4 and 6, respectively; since the scanning operation is performed VWithin.the-'beginning portion of the blue lter 6.

`represented ai; |-29-in- Figure 6. Y 15 During the next field cycle, the video signalsv 96 through. |00# will produce light which is visible through the blue filter H6. The blue component Vof the topwhite part of theY object isv represented at |22 in- Figure `6^. Due tothe video signals: 91, the red portionofv the object arearWill supply a small amount of light which will cause this portion of the objectI to appear faintly blue as indicated at |25 in Figure 6 due to the color carryover by reason of the incomplete discharge of the corresponding part ofthe target electrode of the pick-up tube in the preceding eld scansion interval. The video signals 98 corresponding to blue in the object area will cause the blue part of the received image to appear quite blue through the filter ||6 as represented at |25 in Figure 6. The green part of the object' area will appear at the receiver in a faint bluish tone represented at |32 in Figure 6 due to the low intensity video signals 99 generated by reason of the trailing position 46 of the cathode ray beam with respect to the opaque portion 1 of the color lter assembly represented in Figure l. In the next (or green) eld cycle, video signals Ill-I through |05 will produce light at the receiver tube and the green component of the top white part of the object area is represented at |23 of Figure 6. Both the red and blue portions of the object area Will appear slightly greenish due to video signals |02 and |03 respectively and due to the light generated by these signals being observed through the green lter 8. These portions are represented in Figure. 6 at |30 and |21, respectively. The green portion of the object area will be reproduced at the receiver and Will appear predominately green as in |28 in Figure 6 due to the video signals |04 and the observation of the light produced thereby through the green lter I8. The next field cycle (red) shown in Figure 5 will produce results similar to those described above inv connection with the first rleldv cycle (red).

From the above, it may be seen that the top (and the bottom, as Well) White portion ofthe object area Will appear' White due to optical blending of the red, blue and green colors |2, |22 and |23 respectively of'Figure 6. Vrlhe red portion of the object area, rather than appearing with a bluish tone as in Figure 4, will be a proper red colorsince the bluish tinge present in Figure 4 vwill be eliminated by the deliberate addition of a green tinge corresponding to |55@ in Figure 6. The faint bluish tinge |25 of Figure 6' (which corresponds toV the faint blue tinge inuFigure 4) when combined with the deliberately added greenish tinge |353 together with a slight amount of red, result in the optical eiect of a pure red, plus a small component of White. AThe small component of WhiteV is not sulicient to cause the red areato appear Washed out or pale due to the characteristics of the receiver other color or combination of colors or tones.

rcolor-lter disc or drum.

In the blue portion of the object area at the receiver, the greenish tinge |27, due to pick-up or camera tube characteristics, when combined with the reddish tinge |3| which is deliberately added by the phase relationship of the color filter assembly with respect to the scanning operation, in combination with a small amount of the blue |-25,.results in the production of `a proper blue color with a small white component. A similar combination and result occurs in the green portion of the object area with the effect that a proper green color is produced with a small component of white.

ABythis arrangement, it may, therefore, be seen that proper colors of red, blue and green may be produced at a television receiver, even when tubes operating on a storage' principle are used andeven though each field scanning cycle in such tubes does not completely discharge the target electrode, by phasing the color filter assembly such that the scanning operation takes place in the initial portion of the next succeeding'color filter segment of the assembly at the transmitter, i. e., when the scanning operation occurs a predetermined distance following thev lineof demarcation between adjacent filter segments.

' Although an object area is shown which includes white, red, blue and green, it is to be .understood that the present invention, both in theoryv and practice, is equally applicable to any If the pure colors red, blue and green can be reproduced'with properV fidelity, then virtually any other color or tone can be reproduced with equal `fidelity, with intelligent choice Aof filters and filter numbers.

vIn Figure 1, opaque portions 5, 1, 9 and are ,f

shown separating the lvarious segments of the color filter assembly. These opaque portions or fspokes" were shown in this figure in order to assist in the explanation of the theory of operation of the present invention by comparing the ation is so performedV that light of only one color --is permitted to fall uponv the light responsive electrode between successive scanning operations. In accordance with the present invention, actually light of two different colors is permitted to fall upon the light responsive electrode of the pick-up tube between successive scanning operations since the filter assembly is so phased that a short exposure of the next succeeding color takes place prior to the actual scanning operation. Actually, in carrying out the present inf5, v'ention, the opaque portions 5, 1, 9 and are unnecessary from an operational standpoint, but,

v'if desired, they may be included from a construcn tional standpoint, since generally` some rigid physical means is necessary to support the individual filters as, for example, the spokes of the If the disc or drum is made of Lucite or some other transparent materialwith the filter segments cemented or other- `wiseattached thereto or imbedded therein then,

18 in fact, no portion of the effective part of the color filter assembly need be made opaque and the individual adjacent filter segments may be abutted immediately against each other.

As indicated above, the` amount of color carryover` or contamination due to charge carryover Within suitably designed television pick-up tubes of the storage type is not excessive and may vary in the range of from 5 to 15%. Although the percentage of color carryover may seem trivial, due to the sensitivity of the eye to departures from color purity, the bluish tinge, for example, that is imparted into red objects is quite noticeable and, in fact, renders the reproduction of pleasing and natural flesh tones difiicult. If the color sequence is changed to red, green, blue then iiesh tones become greenish rather than bluish and neither effect is particularly desirable.

In view of the fact that the percentage of color carryover is, in fact, low, only a srnall percentage of color need be injected for compensation to restore. comp-lete color fidelity. Since restoration of color fidelity can be accomplished through the introduction of proper tones in small percentages, the phase adjustments of the color lter assembly at the transmitter becomes somewhat critical. For example, if only a 5% lag of the scanning cathode ray beam at position 48 (i. e., 5% of the red filter IE!) is sufcient to compensate for the greenish tinge that is imparted into blue objects, then naturally, the phase relationship of the filter assembly at the transmitter with respect to the cathode ray beam becomes somewhat critical in order that just the proper percentage of compensating color may be added to effect the desired results. I

In order to render the phase adjustment of the scanning filter assembly less critical, several suggestions are shown by way of example in Figures 8 through 12, which represent developments of filter drums or discs that may be used at the transmitter. In each'of Figures 8 through 11, no opaque portion or spoke (corresponding to the usual spoke) is provided between adjacent filter elements since, as explained above, no such provision is necessary. If, in actual practice, a spoke is required for mechanical reasons, the presence of the spoke, even ifvopaque, does not interfere with the exercise of the present invention. In

vorder to render the phase adjustment less critical,

the region in the leading portion of each filter segment may be altered. `The direction of filter motion of the filters represented ineach of Figures 8 through 12 is represented by an arrow associated with each figure. In Figure 8, for example, blue,

. red and green lter segments |45, |42 and |44,

lis constructed iri a similar fashion. The leading 'portion of each filter segment is provided with a plurality of fine or thin parallel adjacent opaque linesthat extend parallel to the junction of the filters. VThese parallel opaque lines occupy the `region marked |45 in the blue filter |40 and may extendv over approximately 20% of the leading portion of that filter. The ratio of the widths of the opaque lines in region |45 tothe intervening portions of the blue filter |40 may be any preferred ratio such as 1:1 or 2:1 Ibut the ratio should be so chosen as t0 render the phase adjustment sufciently non-critical as to make the phase control readily adjustable. Within the Vregion |45, it is understood that the parallel portions between the thin opaque lines is of blue lter material similar to the blue filter |40 and preferably a part thereoi` with the opaque lines drawn or otherwise applied thereto. These lines may be ruled or otherwise positioned on the filter element per se, or aixed in any appropriate manner. A similar band |46 of opaque lines is located in the leading portion of the red filter |42 and a similar arrangement is provided inthe leading portion of each other segment of the color filter assembly. Due to reduced transparency because of the presence of the opaque lines, phase adjustment by means of the control 22 shown in Figure 7 is rendered'less critical in order to obtain the desired compensation for color carryover and in order to effect the desired purity of color at the receiver.

A modi-hed arrangement for producing the same result is shown in Figure 9 Where blue, red a-nd green filters |50, |52 and |55 are provided. The leading edge of the blue filter is represented at the point Whereas the trailing edge of the preceding red filter is represented at point |55. Between points |5| and |55 is an opaque region |51, the purpose of which will be explained later. The boundary between the red filter |52 and the greenriilter |54 is represented at point |56.

In some television pick-up tubes of the storage type, the light responsive electrode is made of certain chemicals that render them particularly sensitive in the red portion of the spectrum. If, for example, the signals produced during the scanning of a red eld are considerably higher in relative intensity than are the signals generated during the green or blue fields, then color balance due to non-uniformity of color response of the pick-up tube can be accomplished by reducing the amplitude of the signals generated during the scanning of the red field by reducing the exposure time. This may be accomplished by providing the opaque portion |51 between the end |55 of the red iilter |52 and the leading edge 15| of the blue filter |50. By proper choice vof the width (i. e., the dimension in the direction of filter motion) of the opaque portion |51 a satisfactory `color balance can generally be obtained. An

arrangement for accomplishing this same purpose, is shown and described, for example, in Somers Patent No. 2,429,849, issued October 28, 1947, and Somers Patent No. 2,478,598, issued August 9, 1949.

In order to render the phase adjustment less critical, regions |58 at the leading edges of each of the blue and green filters, are provided with a series ofV parallel diagonal opaque lines as indicated in Figure 9 and if, for example, the width of the opaque lines is made equivalent to the Width of the filter portion intervening the lines, the sensitivity of the phase control is made onehalf as critcal. A corresponding region or portion of the leading edgeof the red filter segment |52 (or segments, if more than one set of iilters is employed) of the color filter assembly is similarly provided with a band or region |59 including lparallel diagonal opaque lines, but, due to the fact that the television pick-up tube is considerably more responsive to wave lengths in the region of red light, the ratio of the lines or opaque portions `to the filter portions is increased over the ratio used in the preceding or leading portions of the blue and green iilter segments. For example, the widths of the opaque lines in the region |59 associated with the red filter may be 2 times the Widths of the intervening iilter portions (as com.-

20 pared with equality of widths in the case of" the blue and green iilter segments).

A further modification of a color -lter assembly Which may be used in the present invention and which will reduce the sensitivity of the phase control is shown in Figure l0. In this particular figure, blue, red and green filter elements |50, |62 and |64 are provided. The boundary or junction of the bluefilter |65 into red iilter |52 is represented at point I5! While the boundary between the red filter |62 and the green lter |54 is represented at the point |63. In the region of the leading portion of each lter element is shown a shaded area |65 which includes, in addition to the underlying filter, a light Wedge having its most opaque portion adjacent the boundary between iilter elements, 'as at points |51 and |53, and 'its most transparent portion parallel to these boundaries but positioned most removed therefroml- This Vlight wedge is preferably a neutral nlter which Vvaries in transparency in the direction Aof rotation of the -lter assembly. For example, the transparency may be most dense in that portion of the region |55 that is adjacent the junction Mil and least dense at the opposite edge of the region |65. Through Vthe use or a light wedge of this nature, very small percentages of 'compensating color may be lcontrolled with` ease, since the most dense portion of thewedge Would then be controlling, Whereas high 'percentages of 'compensating color would require that the beam be n a more transparent portion of the light Wedge. Y

A further arrangement is `shown in Figure l1 which is effective for reducing the sensistivity of the phase control but this arrangement .is useful only in color filter Yassemblies of the disc type or of artype where there is radial component of motion (i. e., in the line deflection direction) as the color filterassembly is rotated.v 'The arrangement shown in Figure 1l would not .be satisfactory .for drum type filter assemblies where the motion is solely in the eld deflection direction.

In Figure l1, blue, red andV green vfilter elements |10, |12 and |14 are. provided with the leading edge of the bluelter at point [1|: and the trailing .edge of the 'red filter at point. |15. The junction orboundary .between the red .lter I 12 and the greenlter |14 is represented at the point |15. Intermediate points|1| and |15 there is an opaque portion |11. The purpose for this opaque portion is to reduce the elective sizeof the red filter element |12 tov equalizey or properly proportion the strengths. or the intensities of the produced video-'signals for -all colors, relative to each other, asv Was the casein connection with the opaque portion |51shown anddescribed in connection with Figure 9. The leading` poi;- tion of all the lterel'ements is providedV with the region in which. opaque lines. arev provided, the lines extending to the. lead-ing edge yof each particular filter element.. The region |18, for example, is. .provided with. a` series of short opaque. lines, as. represented inrFg-ure 1i, and the same ratio of opaque line Width4 to intervening lter Width used. in the arear |18 may-also be employed for all of the blue and green lters (unless ysome relative signal strength compensation is required as between these two colors). The region |19, associated with theleading-edge lof the red filter |12., has the same general conguration but a diierent ratio of line widthto in,- tervening lter Width. The purpose of the 'diier- 21 ent ratio is exp1ained in connection with a similar arrangement in the area |59 of Figure 9. As stated above, the suggested modification of Figure 11 would be unfit for a drum type color filter assembly since the injection of the compensating color would'take place only along vertical bands in the image and there would be no reduction in phasing sensitivity in the bands. If the scanning took place within the region of the short opaque lines, as isthe preferred arrangement to render the sensitivity of phase control less critical, then color compensation and a resultant color purity would exist only over those vertical portions wherein light would be admitted through the filter portionv between the parallel opaque lines.

In accordance with the present invention, color purity may be obtained, as expressed above, by the deliberate injection of a small percentage of color to compensate for the color carryover due to the storage characteristics. of the tube and the incomplete discharge of the target electrode during a single field scansion interval. It is not necessary that this small percentage be injected by scanning a predetermined short distance following the line of separation or junction of the filter elements. This injection of color to bring about color purity can be accomplished in a color filter assembly wherein the scanning operation does take place at the line of separation of adjacent filterelements, or under the shadow of the spoke where an opaque boundary or spoke is provided between adjacent filters, by providing each lter element with a strip of a predetermined width and of the required color. Such an arrangement is shown in Figure 12. In Figure 12, blue, red and green filters |88, |82 and |84 are provided and if the color sequence is red, blue, green as indicated in Figure 12, then the blue lterf |80 will be provided with a narrow green filter portion |8|, the red filter |82 will be providedgwith a narrow blue filter portion |83 and the green filter |84 will be provided with a narrow red filter portion |85. To assist in explainingthe operation of such a filter, opaque portions |86 or spokes are shown separating the adjacent filters. In this particular arrangement, the scanning operation may take place within the shadow of the opaque portion |35 and, with a filter assembly such as shown in Figure l2, a

result will be accomplished which is identical to the results accomplished when the scanning operation takes place a predetermined distance 'following the junction of adjacentl filter elements. For example, if the scanning for a particular field cycle falls under the shadow of the opaque portion |86 separating the red filter |82 into green filter |84 (scanning beam at point |81) then video signals will be generated corresponding to signals |E|| through |05 of Figure 5 ifan object such `as representedin Figure 2 is scanned. The red signal |82 will result by reason of the narrow red filter |85, the blue Video signal |03 will result by reason of the preceding blue filter element |88 and the residual charge present on' the target electrode of the tube, while the video signal |04 (representing green) will be generated due to the exposure through the green filter |84. Such an arrangement is entirely `-feasible and proper selection of the widths of the compensated lter elements |8|, |83, |85 can result in the achievement of proper color fidelity. -Such an arrangement is not whollyvdesirable for the' simple reason that there is provided no means for adjusting the amount of color added in" order to compensate for the undesired color el (i 22 carryover. The extent of the color that is added for compensating purposes is determined by the widths or dimensions of the filter strips |8I, |83

and |85 in the direction of filter rotation whereas, in arrangements such as are represented, for f example, in Figures 8, 9, l0 and 11, any desired or required amount of color injection may be produced in order to assure the desired results by merely shifting the phase relationship of the color filter assembly with respect to the scanning operation yby means of the phase control 22 of Figure 7.,

In regard to Figure l2, it is not necessary that thecompensating filter strips |8|, |83 and |85 be located intermediate the leading and trailing edges of the filters |88, |82 and |88. They may, of course, be positioned at the trailing edges of the filters or at the leading edges. Regardless of their position, it is to be understood that they are not positioned on top of the principal filter but are separate narrow filter inserts. In the case shown in Figure 12, blue filter |80 is, in fact, composed of two parts, separated by the compensating filter strip |8|.

So far as compensation of color carryover is concerned, it is theoretically immaterial where the stripsV |8I, etc., are located so long as they precede the scanning operation in point of time. Actually, this is true onlyfin pick-up tubes having complete or full storage characteristics as in the orthicon. In the image orthicon and in the iconoscope, where secondary electrons are generated (but may be insufficient to cause complete cancellation of the residual charge image), stor-` age is not 100% and the strips |8|, etc., of Figure l2 should be positioned at or near the trailing edge of a filter element. Rather than provide these insert strips it is, therefore, preferable to use a filter assembly such as shown in one or' another of Figures 8 through 11 and to so phase the color filter assembly that the scanning operation takes place a predetermined distance following the line of demarcation between filter elements.

In Figures 8 through ll are shown various arrangements to render the phase adjustment less critical by reducing the transmission efficiency of the `leading position of each filter element. Under certain conditions, it is unnecessary to provide a series of opaque lines as in Figures 8, 9 and 1l or a light wedge as in Figure 10 to 'accomplish the result of producing a less critical phase adjustment. This can be alternatively accomplished by providing the color filter assembly with an opaque portion or spoke intermediate adjacent filter elements and by so positioning the assembly with respect to the optical lens system, of the television pick-up device that a partial shadow or penumbra is produced. Within the region of this penumbra the phase adjustment will be less critical since the optical eiciency of the system is reduced. For optical reasons, the actual width of a complete shadow on the light responsive electrode will be less than the width of the opaque portion between adjacent filter elements and this complete shadow wil1 be bounded on each side by a penumbra. The width of the penumbra is a function of the position of the filter assembly with respect to the lens system, the focal length of the lens and the lens diameter. By proper choice of these parameters, the extent of the penumbra on each side of the complete shadow can be regulated to cover the desired portion of the filter segments in order that the range of the lens.

less critical phase adjustment is sufficient to accomplish the purpose. 'Ihe scanning operation would then be carried out in the trailing penumbra, i. e., following the most complete shadow, and in the leading or initial portion of the next succeeding filter element. This penumbra or partial shadow is not uniform in intensity but is similar in effect to the use of a light wedge in which the least amount of light or lowest transmission eiciency is nearest the complete shadow, while the greatest amount of light or highest eiciency is most removed from the complete shadow. Accordingly, the phase adjustment becomes relatively less critical as smaller values of compensating color are required, thus assisting materially in the actual adjustment of the phase relationship. The penumbra produced over the trailing portion of the preceding filter element, although unavoidable, does reduce to a slight extent the overall optical efficiency of the system, but with the increased sensitivity of modern television pick-up tubes, this slight reduction in sensitivity `may be readily tolerated.

Such an arrangement is particularly useful in studio set-ups where the lighting conditions are substantially uniform and under these conditions, lenses having approximately the same focal length and effective diameter are used consistently. Under such conditions, where the focal length of the .lens as well as its eifective diameter are not frequently altered so far as any particular camera is concerned, the use of penumbra can very readily be put into practice since the width or extent of the penumbra will remain constant, but can be altered by shifting the position of the filter assembly with respect to Naturally, if it should become necessary to stop down the lens or reduce its effective diameter, the extent of the penumbra would correspondingly be reduced.

In view of the foregoing, it is, therefore, clear that color contamination or color carryover as a result of the inherent operation of full storage type television pick-up tubes, or storage type tubes wherein a residue of the charge image is carried over from one field to the next, can be completely compensated for, and in addition, the color hue of the reproduced image can be improved, by the deliberate injection ofr low intensity video signals representing a second color component into each television field. This is accomplished by exposing the light responsive electrode to light of two different colors (and for different time intervals)` between each successive scanning operation. This is`V preferably brought about by so phasing the color iilter `assembly with respect to the scanningV operation' thatthe position of the scanning cathode raya` beam is located a predetermined short distance following the line ofseparation or demarcation between adjacent ii'lter elements. If a spoke or opaque portion intervenes between adjacent lt'er elements, then color purity can be obtained and color carryover eliminated Yby scanning a predetermined distance following the shadow cast by the opaque portion intermediate adjacent filter elements.

Having now described my invention, what is desired to be secured by Letters Patent is:

l. The method of operating a color television transmitter wherein a storage type `cathode ray television pick-up tube having' a target electrode is provided and wherein theV target electrode is notcompletely discharged by a single scanning operation of a cathode ray beam which .comprises the steps of producing a charge on the target electrode in accordance with the light values of a particular component color of the object area, producing a further relatively small charge on the target electrode in accordance with the light values of a different `particular component color of the object area between cach successive Scanning operation, and scanning the target area to produce video signals according to the charges so produced, thereby to compensate for the lackof incomplete discharge of the target electrode by each individual scanning operation. A

2. The method of operating a trichromatic sequential color television transmitter wherein a charge storage target electrode is cyclically scanned by cathode ray beam to produce color television image signals, Ywhich comprises the steps of producing image signals representative of the light values of a predetermined different color for each successive scanning cycle, in herently producing low intensity image signals representative of the light values of the color for which image signals were produced in the immediately preceding scanning cycle due to the .in-

ability of the cathode ray beam to completelyv discharge the charge storage target electrodeI during a single scanning cycle, and deliberately producing low intensity image signals of 'adjustable magnitude representative of the light values of the color for which image signals will be.pro. duced in the next following scanning Gycle, thereby to compensate for the color carryover effects that result from inherently produced image signals of low'intensity.

3. The method of operatingatrichromatic sequential color television transmitter wherein'ra charge storage target electrode is cyclically scanned by a cathode ray beam to producelimage signals and wherein the charge on the target electrode is not completely removed by a single scanning operation, which comprises the steps of producing television image signals during. each scanning cycle representative primarily of the light values of one predetermined color, inherently producing. television image signals of low .intensity during each scanning cycle representative of the light values of a second predetermined color, and deliberately producing television image signals of low'intensity and adjustable magnitude during each scanning cycle representative of the light values of a third predetermined color, Vthereby to compensate for the lack of color fidelity due to color carryover resulting from the inherently produced low intensity image signals.

4. A sequential tricolor television transmitter including a television pick-up tube of the storage type wherein a cathode ray beam is developed and wherein a charge storage target electrode` is provided', includingv a color lter assembly having .arranged sequentially thereon filter elementsl corresponding to the Yselected three component colors, means for positioning the color filter assembly in the optical light path of the television Apick-up' tube, means for rotating the color-,filter means for so phasing the color lter assembly that. the line of separation between adjacent -color filter elements of the color lter assembly precedes, in point of time, the position of the developed cathode ray beam so that-the scanning operation takes place following. the line of separation between the adjacent color lter elements thereby to produce, during each field scanyaes-'zopas with respect to the scanning operation that the particular line scanned on the storage electrode occurs a predetermined relatively short interval after the boundaries between adjacent filter elements has effectively passed over that part of the storage electrode where the scanning operation is being performed.

ll. In a sequential tricolor television apparatus including a television pick-up tube of the storage type having a charge storage target electrode which is sequentially scanned in a plurality of e,

substantially parallel paths to produce television video signals but wherein the charge on the target electrode is not completely removed by a single scanning operation, the color filter assembly including sequentially arranged color lter 5,

elements corresponding to selected component colors of the tricolor system, means for positioning the color filter assembly in the optical light path of the television pick-up tube, means for rotating the color filter assembly so that the lines of demarcation between adjacent component color filter elements lie substantially parallel to the lines scanned on the target electrode, means for rotating the color iilter assembly in synchronism with the scanning operation of the target felectrode so that the rate of progress of the line of demarcation of the color filter elements correspends substantially to the rate of progress of the scanning operation, means for shifting the relationship of the color filter assembly and the i scanning operation such that the lines of demarcation precede, by a small adjustable amount, the particular lines scanned on the target electrode whereby, in addition to the generation of video signals corresponding primarily to the light values of one particular color, video signals are generated in low intensity and in adjustable magnitude corresponding to the light Values of another particular color, thereby to compensate for the lack of color fidelity resulting from color carryover due to incomplete discharge of the target electrode by a single scanning operation.

12. In a sequential tricolor television apparatus including a television pick-up tube of the storage type having a charge storage target elecf trode which is sequentially scanned in a plurality of substantially parallel lines repeated at a selected eld frequency rate to produce television video signals but wherein at least a small portion of the charge on the target electrode is retained in the target following each .single scanning operation, the color filter assembly including sequentially arranged color lter elements corresponding to the component colors of the tricolor system, means for positioning and rotating the colorlter assembly relative to the pick-up tube so that'the lines of demarcation between adjacent color iilter elements remain substantially parallel to the lines scanned on the target electrode,l means so adjusting the relationship of the color e :but wherein video valuesfotone: particular color,l low intensity video signals'are generated corresponding to. the light values of another particular color, thereby `to compensate for the lack' of color fidelity. resulti'ngfrom color carryover due toL incomplete :discharge of the target electrode by asingle scanning operation.

13. In a sequential tricolor television transmitting system including a storage type image pickup tube having a. charge storage target electrode, a'component color lter assembly positioned in the optical light path of the pick-up tube for sequentially changing the color of the light pro.- jected into said tube whereby color television video signals'may be generated. for each scanning cycle corresponding predominately to light values of one particular component color, signals are inherently generated in low intensity representativeof a second component color dueto charge carryover at the target electrode and the incomplete charge cancellation for each successive scanning cycle, and means for so phasing the color filter assembly with respect to the scanning operation that, in each scanning cycle, video signals are also generated in low intensity corresponding to the light values of the third color component whereby the effects of color contamination and color carryover due to incomplete charge cancellation-are substantially .nullified.

14. In a sequential tricolor television transmismitting system including a storage type image pick-up tube having a charge storage target electrode, a component color iilter assembly positioned in the optical light path of the pick-up tube for sequentially changing the color of the light projected into-said tube to permit the production of color television video signals for each scanning cycle corresponding primarily to light values of one component color, but wherein low intensity video signals are inherently produced corresponding to light values of a second-component color due to charge carryover at the target electrode from one scanning cycle into the next, and means for so phasing the color lter assembly with respect to the scanning operation that, in each scanning cycle, low intensity video signals are also produced corresponding to the light values of a third color component whereby the lack of color fidelity due to charge carryover at the target electrode is substantially overcome.

15. In a sequential tricolor television. apparatus the combination which comprises an electron scanning device having a charge/storage electrode; means for cyclically scanning the charge storage electrode with said scanning device in two dimensions in a plurality of substantially parallel lines, a rotatable color filter assembly having a plurality of component color lter elements of different optical characteristics corresponding to the three selected component colors into which the image is analyzed, said assembly being positioned and arranged in the path of light from the object area to the scanning device with the boundaries between adjacent iilter elements substantially parallel optically with the lines scanned on the storage electrode, said light passing through said individual elements as the aS- sembly rotates to progressively change the color of light directed upon the scanning device at substantially the same speed at-which the lines are scanned, and means for exposing the scanning device to light of two different colors between successive scanning cycles, the exposure to ning cycle, low intensity color television video signals representative of the color of the next succeeding color filter element.

5. A sequential tricolor television transmitter including a television pick-up tube of the storage type wherein a cathode ray beam is produced and wherein a charge storage target electrode is provided, including a color lter assembly having sequentially arranged component color lter elements, means for rotatably positioning the color filter assembly in the optical light path of the television pick-up tube, and means for so phasing the color lter assembly with respect to the scanning beam that the line of separation between adjacent color filter elements of the color lter assembly precedes, in point of time, the position of the produced cathode ray beam so that the scanning operation takes kplace in the leading portion of the next succeeding color filter element thereby to produce, during each field scanning cycle, low intensity color television video signals representative of the color of the next succeeding color filter element.

6. A tricolor sequential television signal translating system comprising a television pick-up tube having a charge storage target electrode, means for successively scanning said target electrode with `an electron beam in a series of parallel lines, a color filter assembly interposed in the optical light path of the television pick-up tube and between the target electrode and the object area, said color filter assembly including a plurality of lter elements corresponding to the three selected component colors in which the image is to be analyzed, means for moving said color lter assembly so that the lines of color demarcation thereof between adjacent filter elements remain substantially parallel to said lines of Said series, means for so phasing the position of the color lter assembly with respect to the scanning electron beam that the color of light associated with each line is changed a predetermined adjustable interval prior to the instant that such line is scanned whereby color television image signals will be generated corresponding primarily to the light values of a predetermined color and also whereby low intensity color television image signals of adjustable intensity will be generated corresponding to the light values of another predetermined color.

7. A tricolor sequential television signal translating system comprising a television pick-up tube having a charge storage target electrode, means for cyclically scanning said target electrode with an electron beam in a series of parallel lines, a color filter assembly interposed in the optical'path of the television pick-up tube, said color filter assembly including a plurality of component color filter elements, means for moving said color filter assembly so that the lines of color demarcation thereof between adjacent filter elements remain substantially parallel to said lines of said series, means for so phasing the position of the color filter assembly with respect to the scanning electron beam that the color of light associated with each line is changed a predetermined interval prior to the instant that such line is scanned, said predetermined interval being short as compared with a scanning cycle whereby color television image signals, in different relative intensities, will be generated corresponding to the light values of two predetermined colors.

8. In a sequential tricolor television transmitting apparatus which comprises an electron 26 scanning device of the storage type having an image receiving area associated therewith, means for focussing a two dimensional light image of an object field on said image receiving area, means for scanning a charge storage target electrode associated with the image receiving area in two dimensions in a plurality of side by side lines, means for progressively changing the color aspect of the light image including a rotatable color filter assembly having a plurality of component color filter elements arranged thereon with boundaries between the individual filter elements, said assembly being positioned and arranged in the path of light rays forming said image with the boundariesy between said filter elements substantially parallel optically with the scanned lines, means for rotating said color filter assembly in substantial synchronism with the low frequency scanning of the target electrode, means to so phase the color filter assembly that the boundaries between adjacent filter elements precede, in point of time, by an adjustable amount, the line being scanned as the boundaries successively traverse the image receiving area and asV the scanning operation progresses across the target electrode whereby color television video signals are produced for each scanning operation corresponding to the light values of two different component colors but in which the relative magnitudes of the signals representing the two colors are considerably different depending upon the amount by which the boundary between individual lilter elements precedes the line scanning operation.

9. In a sequential tricolor television transmitting apparatus which comprises an electron scanning device of the storage type having a charge storage electrode, means for scanning the charge storage target electrode in two dimen-Y sions in a plurality of substantially side by side lines, means including a rotatable color filter assembly having a plurality of component color filters arranged thereon with boundaries between the individual filter elements, said assembly being positioned and arranged so that images of the boundaries between said filter elements remain substantially parallel optically with the scanned lines, means for rotating said color lter assembly in substantial synchronism with the low'frequency scanning of the target electrode, means for phasing the color filter assembly so that each boundary between adjacent lter elements is advanced, in point of time, with respect to the line being scanned, the degree of advance being a small percentage of a lter element, whereby color television video signals are produced for each scanning operation corresponding to the light values of two diierent colors but in which the relative magnitudes of the signals representing the two colors are considerably dilerent depending upon the degree of advance, and means for altering the phase relationship of the filter assembly to change the degree of advance of the assembly.

10. In a sequential tricolor television apparatus the combination which comprises an electron scanning device having a charge storage electrode, means for scanning the charge storage electrode with said scanning device in two dimensions in a plurality of substantially parallel lines, a rotatable color lter assembly having a plurality of component color filter elements, having different optical light transmitting characteristics, said assembly being positioned and arranged in the path of light from the object area 29 one of the two colors being long as compared Number with the exposure to the other of the two colors. 2,310,337 O-TTO H. SCHADE. 2,384,260 2,413,075 REFERENCES CITED 5 2,416,918 The following references are of record in the 1435963 le of this patent:

UNITED STATES PATENTS Number Number Name Date 555,213

1,278,211 Raleigh Sept. 10, 1918 Name Date Anderson Feb. 9, 1943 Goldsmith Sept. 4, 1945 Schade Dec. 24, 1946 Goldsmith Apr. 4, 1947 Goldmark Feb. 17, 1948 FOREIGN PATENTS Country'` Date Great Britain Aug. 10, 1943 

